The Job Description is less about helping you find the people you want and more about filtering out the people you don't want. On sites like elance and staff.com the people you want will find you.

So let's start with some key points about Job Descriptions:

• Long and highly specific descriptions don't work as well as you'd expect when outsourcing talent - especially in the philippines. They won't even apply if there is even a single item them feel they don't meet (e.g. 4 years of ruby development when a perfect qualified candiate only has 3).
• Don't be vague - things like "passionate about success", "able to work well with others". Only put down actionable items. Keep it clear and concise - 3 points is perfect to get people in and you can filter them later.
• Lack of contact information and payment scale - lot of firms will leave out payment scale hoping to win over candidates during the interview process, but you'll end up wasting everyone's time and becoming frustrated. If you can only afford 48K per year, says so.
• Use the code word trick - I've done this several times to really help filter out potential candidates and quickly identify the concise attentive ones. Somewhere in the middle of the job description, tell them to reply with an email that has your code word in the subject line. This way you can go into your email client and set up a filter to only look at new emails containing your keyword in the subject line.